case <-errCh:
			errorsCount++
			// All servers returned error - return failure.
			if errorsCount == len(h.resolvConfServers) {
				scope.Infof("all upstream failed")
				return serverFailure(req)
			}
		}
	}
}

func serverFailure(req *dns.Msg) *dns.Msg {
	failures.Increment()
	response := new(dns.Msg)
	response.SetReply(req)
	response.Rcode = dns.RcodeServerFailure
	return response
}